Mobile terminals, such as mobile phones, communicate in various systems (Radio Access Technology: RAT) in order to, for example, promote efficient use of radio waves and increase communication speed. Examples of communication systems in practical use for mobile phones include Global System for Mobile (GSM), Wideband Code Division Multiple Access (W-CDMA) and Super 3G (Long Term Evolution: LTE).
Upon introduction of a new communication system in an area in which another communication system is operating, it is desirable that both communication systems can operate together. An exemplary system therefor is a RAT handover process by which different communication systems are switched over in real time to provide high quality and high speed wireless communication in various communication environments (see Japanese Laid-Open Patent Publication No. 2003-333660). In the RAT handover process, a communication level is measured for each communication system before a handover is made between base stations operating under different communication systems on the basis of the measured level.
Mobile terminals, such as mobile phones, which are required to achieve high performance and reduced size at the same time, are often provided with a single antenna common to a plurality of communication systems. In such a configuration, gap sections in which no data communication is made are interposed between radio frames transmitted under a communication system in operation (hereinafter, referred to as a “first communication system”). At the same time, quality of communication under a communication system not in operation (hereinafter, referred to as a “second communication system”) is assessed in the gap sections (see Japanese Laid-Open Patent Publication No. 2000-078640).
The related art technology described above, however, has the following deficiency. In the event that the length of the gap sections in the radio frames of the first communication system is insufficient, quality of communication under the second communication system cannot be assessed appropriately and thus a handover to another communication system cannot be made accurately. In most cases, the gap sections of the first communication system are dedicated to assessment of quality of communication at different frequencies under the first communication system. Thus, the gap sections are not always long enough to provide appropriate assessment of quality of communication under the second communication system.
When the gap sections of the first communication system are insufficient in length, it is difficult to determine head positions of radio frames of the second communication system in the gap sections of the first communication system. With this configuration, symbols for measurement included in the radio frames of the second communication system cannot be measured accurately. In the event that the radio frames of the second communication system are longer than the gap sections in the radio frames of the first communication system, the symbol for measurement included in the radio frames of the second communication system may be out of the gap sections in the radio frames of the first communication system. Thus, quality of communication in the second communication system cannot be assessed appropriately.